Asteroid may have killed dinosaurs quicker than scientists thought

February 07, 2013|Reuters

* Asteroid impact preceded extinction by 33,000 years

* Previous dating techniques flawed

By Irene Klotz

CAPE CANAVERAL, Fla., Feb. 7 (Reuters) - Dinosaurs died offabout 33,000 years after an asteroid hit the Earth, much soonerthan scientists had believed, and the asteroid may not have beenthe sole cause of extinction, according to a study releasedThursday.

Earth's climate may have been at a tipping point when amassive asteroid smashed into what is now Mexico's YucatanPeninsula and triggered cooling temperatures that wiped out thedinosaurs, researchers said.

The time between the asteroid's arrival, marked by a110-mile-(180-km-)wide crater near Chicxulub, Mexico, and thedinosaurs' demise was believed to be as long as 300,000 years.

The study, based on high-precision radiometric datingtechniques, said the events occurred within 33,000 years of eachother.

Other scientists had questioned whether dinosaurs diedbefore the asteroid impact.

"Our work basically puts a nail in that coffin," geologistPaul Renne of the University of California Berkeley said.

The theory that the dinosaurs' extinction about 66 millionyears ago was linked to an asteroid impact was first proposed in1980. The biggest piece of evidence was the so-called Chicxulub(pronounced "cheek'-she-loob") crater off the Yucatan coast inMexico.

It is believed to have been formed by a six-mile-(9.6-km-)wide object that melted rock as it slammed into the ground,filling the atmosphere with debris that eventually rained down on the planet. Glassy spheres known as tektites, shocked quartzand a layer of iridium-rich dust are still found around theworld today.

Renne and colleagues reanalyzed both the dinosaur extinctiondate and the crater formation event and found they occurredwithin a much tighter window in time than previously known. Thestudy looked at tektites from Haiti, tied to the asteroid impactsite, and volcanic ash from the Hell Creek Formation in Montana,a source of many dinosaur fossils.

NEW DATING TECHNIQUE

"The previous data that we had ... actually said that they(the tektites and the ash) were different in age, that theydiffered by about 180,000 years and that the extinction happenedbefore the impact, which would totally preclude there being acausal relationship," said Renne, who studies ties between massextinctions and volcanism.

He and colleagues were comparing a new technique to dategeologic events when they realized there was a discrepancy inthe timing - the so-called 'K-T boundary' - the geological spanof time between the Cretaceous and Paleocene periods when thedinosaurs and most other life on Earth died out.

"I realized there was a lot of room for improvement. Eventhough many people had locked in their opinions that the impactand the extinctions were synchronous or not, they were basicallyignoring the existing data," Renne said.

The study, published in Science, resolves existinguncertainty about the relative timing of the events, notes HeikoPÃ¤like of the Center for Marine Environmental Sciences at theUniversity of Bremen, Germany.

Renne, for one, does not believe the asteroid impact was thesole reason for the dinosaurs' demise. He says ecosystemsalready were in a state of deterioration due to a major volcaniceruption in India when the asteroid struck.

The asteroid strike "provided the coup-de-grace for thefinal extinctions," Renne said, adding that the theory wasspeculative, but backed by previous ties between mass extinctionevents and volcanic eruptions.

About 1 million years before the impact, Earth experienced six abrupt shifts in temperature of more than 2degrees in continental mean annual temperatures, according toresearch cited by Renne and his co-authors.

The temperature swings include one shift of 6 to 8 degreesthat happened about 100,000 years before the extinction.

"The brief cold snaps in the latest Cretaceous, though notnecessarily of extraordinary magnitude, were particularlystressful to a global ecosystem that was well adapted to thelong-lived preceding Cretaceous hothouse climate. The Chicxulubimpact then provided a decisive blow to ecosystems," Renne andhis co-authors wrote in Science.